The permanent magnet excited electric machine according to the invention may be an electric motor or a generator for generating current or also a combination of both, which selectively operates as motor or as generator. The electric machine according to the invention may be a rotary or a linear machine. In the following, reference will be made mainly to rotary machines, however, all statements hold analogously for linear machines as well.
The electric machine according to the invention preferably is commutated electronically, i.e. it is connected in operation to electronic functional units by means of which current can be supplied to the winding coils of the winding system for a respective suitable time phase or by means of which current can be withdrawn from the winding coils in the respective suitable time phases. In the following, reference will be made predominantly to electronically commutated machines, but a large part of the statements made applies analogously also for machines that are not commutated electronically.
With respect to the electric machine according to the invention, there are the following two basic design possibilities: either the stator part is provided with the winding coils of the winding system and the moving part is provided with the permanent magnets; this design has the advantage that no current for the winding coils has to be supplied to the moving part and no current has to be discharged from the winding coils, respectively. However, it is also basically possible in the contrary to provide the stator part with the permanent magnets and the moving part with the winding coils.
In permanent magnet excited electric motors, electric current in a specific amount and with a specific sign is supplied to each of the winding coils for certain time phases. As soon as the rotor rotates, the permanent magnets (positioned e.g. on the rotor) induce a voltage in the winding coils (positioned e.g. on the stator); this induced voltage usually is briefly referred to as Ui or EMF.
In the development of such machines in the past, great efforts were made to improve the performance and efficiency of such machines. Despite this, there are mostly considerably losses arising during operation that do not only affect the efficiency of the electric machine, but also entail additional problems, such as e.g. strong heating of the machine, resulting in extensive cooling requirements for the machine in its entirety.